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<H2><A NAME="SECTION0002120000000000000000"></A><A NAME="drawing-graph-canvas"></A><a id='l2h-351' xml:id='l2h-351'></a>
<BR>
21.2 Drawing plots on canvas
</H2>
PyChart creates a new canvas object when "<code>area.T.draw()</code>"
(see Section <A href="module-area.html#module-area">6</A>) is called for the first time, and no canvas is yet
created at that moment. You can thus use you own canvas by creating a
canvas <em>before</em> calling the first <code>area.T.draw()</code>, like below:
<P>
<div class="verbatim"><pre>
can = <a href="module-canvas.html">canvas.</a>init("foo.pdf")
...
ar = <a href="module-area.html">area.T</a>(...)
ar.draw()
</pre></div>
<P>
You can also achieve the same effect by passing the canvas object to the
<code>area.T.draw()</code> method explicitly:
<P>
<div class="verbatim"><pre>
can = <a href="module-canvas.html">canvas.</a>init("foo.pdf")
...
ar = <a href="module-area.html">area.T</a>(...)
ar.draw(can)
</pre></div>
<P>
You can also pass a file object (or file-like object, such as
<code>StringIO</code>) to canvas.init. In this case, you need
to define the output format via the second argument.
<a id='l2h-353' xml:id='l2h-353'></a>
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<a id='l2h-352' xml:id='l2h-352'></a><div class="verbatim"><pre>
fd = file("foo.pdf", "w")
can = <a href="module-canvas.html">canvas.</a>init(fd, "pdf")
...
ar.draw(can)
</pre></div>
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<a id='l2h-355' xml:id='l2h-355'></a>
<P>
Naturally, you can write to multiple files by passing multiple
<code>canvas</code> objects to different <code>area.T.draw()</code>. For example,
the below example draws the first chart to <span class="file">graph1.pdf</span> and the next
chart to <span class="file">graph2.pdf</span>.
<P>
../demos/twographs.py
<P>
<div class="verbatim"><pre>
from pychart import *
can = <a href="module-canvas.html">canvas.</a>init("graph1.pdf")
data = <a href="module-chart-data.html">chart_data.</a>read_csv("lines.csv")
ar = <a href="module-area.html">area.T</a>(x_range = (0,100), y_range = (0,100),
x_axis = <a href="module-axis.html">axis.</a>X(label="X", tic_interval=10),
y_axis = <a href="module-axis.html">axis.</a>Y(label="Y", tic_interval=10))
eb = <a href="module-error-bar.html">error_bar.</a>error_bar2(tic_len=5, hline_style=<a href="module-line-style.html">line_style.</a>gray50)
ar.add_plot(<a href="module-line-plot.html">line_plot.T</a>(label="foo", data=data, error_bar=eb, y_error_minus_col=3),
<a href="module-line-plot.html">line_plot.T</a>(label="bar", data=data, ycol=2, error_bar=eb, y_error_minus_col=3))
ar.draw(can)
tb = <a href="module-text-box.html">text_box.T</a>(loc=(40, 130), text="This is\nimportant!", line_style=None)
tb.add_arrow((ar.x_pos(data[6][0]), ar.y_pos(data[6][1])), "cb")
tb.draw(can)
can = <a href="module-canvas.html">canvas.</a>init("graph2.pdf")
ar = <a href="module-area.html">area.T</a>(loc=(200, 0), x_range=(0,100), y_range=(0,100),
x_axis = <a href="module-axis.html">axis.</a>X(label="X", tic_interval=10),
y_axis = <a href="module-axis.html">axis.</a>Y(label="Y", tic_interval=10))
ar.add_plot(<a href="module-line-plot.html">line_plot.T</a>(label="foo", data=data, data_label_format="/8{}%d"),
<a href="module-line-plot.html">line_plot.T</a>(label="bar", data=data, ycol=2))
ar.draw(can)
# Note: can.close() is called automatically for every open <a href="module-canvas.html">canvas.</a>
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<span class="release-info">Documentation released on July 2, 2005.</span>
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